Employee Benefit Plans - Deferred Compensation Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Defined Contribution Plan, Cost	$ 30.3	$ 23.4	$ 21.7
Supplemental Executive Retirement Plan [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred Compensation Liability, Current and Noncurrent	50.4	44.5
Compensation expense (reduction in expense)	7.0	6.5	5.8
Deferred Compensation Plan For Select Group Of Employees [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred Compensation Liability, Current and Noncurrent	124.5	91.0
Compensation expense (reduction in expense)	$ 21.7	$ 5.3	$ 2.9